Investigating N solubility in the host lattice of p-type Al- and N- co-doped SnO2 films with various N2 contents in sputtering gas

Optical Materials xxx (xxxx) xxx

Please cite this article as: Thi Tran Anh Tuan, Optical Materials, https://doi.org/10.1016/j.optmat.2020.110665

Available online 21 November 2020

0925-3467/© 2020 Elsevier B.V. All rights reserved.

Investigating N solubility in the host lattice of p-type Al- and N- co-doped

SnO2 films with various N2 contents in sputtering gas

Thi Tran Anh Tuan a

, Anh Quang Duong b,c

, Nguyen Van Sau a

, Huu Phuc Dang d

, Tran Le b,c,*

a School of Basic Science, Tra Vinh University, 126 Nguyen Thien Thanh Street, Ward 5, Tra Vinh City, Viet Nam b Faculty of Physics & Engineering Physics, HCMC University of Science, VNU-HCM, 227 Nguyen Van Cu Street, Ward 4, District 5, Ho Chi Minh City, Viet Nam c Vietnam National University, Ho Chi Minh City, Viet Nam d Faculty of Fundamental Science, Industrial University of Ho Chi Minh City, No. 12 Nguyen Van Bao, Ward 4, Go Vap District, Ho Chi Minh City, Viet Nam

ARTICLE INFO

Keywords:

p-type transparent conducting oxide

p-type Al- and N- co-doped SnO2 thin film

DC magnetron sputtering

X-ray diffraction

X-ray photoelectron spectroscopy

Time-photocurrent response

ABSTRACT

The Al3+–Sn4+ substitution into p-type Al- and N- co-doped SnO2 films enhances the N solubility in the SnO2 host

lattice. The N solubility in the SnO2 host lattice increased with an increase in N2 content in the mixed sputtering

gas, and the optimum N2 content was found to be 60 %, which corresponds to high film crystal quality and the

lowest resistivity. The Al3+–Sn4+ and N3− –O2− substitution was verified using X-ray photoelectron spectroscopy

(XPS), ultraviolet–visible spectroscopy, energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) patterns. The

SnO2 tetragonal rutile to cubic phase transformation indicated high N solubility in the SnO2 host lattice, while

the Al3+–Sn4+ replacement was also verified by the crystal evolution of a (101) lattice reflection and the

occurrence of the charge compensation effect. The best values achieved for resistivity, hole concentration, and

hole mobility of the film were 6.4 × 10− 3 Ω cm, 6.4 × 1019 cm− 3

, and 15.2 cm2 V− 1 s

− 1

, respectively. The

current-voltage characteristics of films/n-Si heterojunctions under the illumination condition showed the p-type

conductive properties of the films, and photocurrent response of the optimum film/n-Si heterojunction diode

under the illumination condition of monochromatic wavelength light-emitting diodes (LEDs) exhibited a suffi￾cient reproducible cycle and verified the N3− acceptor and VO donor levels in the bandgap.

1. Introduction

Most transparent conductive oxides (TCOs), including ZnO, SnO2,

and ITO, applied in optoelectronic devices serve as n-type conductive

layers, e.g., an electron transport layer for solar cells [1–5], a trans￾parent conductive layer for emitting light diodes [6–8], a transparent

conductive front or back electrode for solar cells [9–13], an n-type

transparent layer for photodetectors [14–16], and photodiodes [17,18].

Although the n-type transparent conductive function of TCOs applied for

optoelectronic devices has achieved great success in science and tech￾nology, a lack of p-type TCOs hampers development for many scientific

and technical fields, especially the transparent optoelectronic field.

For the past several decades, a majority of p-type TCOs are ZnO and

doped ZnO, which have been studied and fabricated using doping group￾IA elements such as Li, Na, and K [19–21] or group-V elements such as P,

As, and Sb [22–27]. However, challenges in eliminating deep acceptors

that do not contribute and interstitial donors that trap conductive holes

have still not been fully overcome, i.e., the reproduction of p-type ZnO is

difficult to achieve [19,28–30]. In literature, ZnO co-doping group-III

elements (Ga, Al, In, B, etc.) and N [31–34] were studied to reduce the

number of unexpected interstitial donors, make acceptors shallower,

and increase acceptor solubility. However, group III elements do not

contribute holes when substituted into Zn. To increase more holes from

the contribution of metal-nonmetal couple or increase long term sta￾bility of p-type ZnO, couples such as Cu–S [35] and Ag–N [36] are doped

in ZnO to improve activation of acceptors.

These limits were controlled in some of the p-type SnO2 films,

including SnO2 doped with Ga [37], In Refs. [38], Zn [39], and N [40],

especially for SnO2 co-doped with Ga and N [41]. An advantage of

group-III elements and N co-doped SnO2 compared to group-III elements

and N co-doped ZnO is the increase in the number of holes for films in

the host lattice, i.e., both increasing N solubility in the SnO2 host lattice

and adding acceptors, which are formed from replacing Sn by group-III

elements, to films. To date, research on Ga- or Al- and N- co-doped SnO2

films [42–44] has indicated that p-type electrical property is improved

compared with that of p-type SnO2 doping single metals. However, the

* Corresponding author. Faculty of Physics & Engineering Physics, University of Science, Ho Chi Minh City, Viet Nam.

E-mail address: [email protected] (T. Le).

Contents lists available at ScienceDirect

Optical Materials

journal homepage: http://www.elsevier.com/locate/optmat

https://doi.org/10.1016/j.optmat.2020.110665

Received 29 January 2020; Received in revised form 25 September 2020; Accepted 16 November 2020